Device for transmitting an optical wave in a structure provided with an optical fiber and method for making same

ABSTRACT

A device for transmitting optical waves has a structure having at least an optical guide element wherein the structure comprises hollow parts or notches ( 9, 10 ) adapted to receive the end parts ( 13, 14 ) of an optical fiber ( 12 ) such that the fiber spans the surface ( 11   a ) of the structure separating the hollow parts and the ends of the optical fiber are respectively optically coupled to optical guide elements ( 7, 8 ) of the structure. The invention also concerns a method for making such a device which consists in etching the notch by cutting off the end of the optical micro-guide. The device is useful for producing optical switches.

The present invention relates to the field of optical wave transmissionin optical guiding structures.

Optical waveguides are used to transmit an optical wave, these usuallyconsisting of optical fibers and/or integrated components which compriseoptical micro-waveguides. The optical fibers generally comprise a core,which transmits the optical wave, surrounded by a tubular cladding, therefractive index of the material(s) making up the core being higher thanthe refractive index of the material making up the cladding. Theintegrated micro-waveguide components comprise a core, in general fortransmitting the optical wave, formed between two layers, the refractiveindex of the material making up the core being higher than therefractive index of the material(s) making up these layers.

Various integrated optical micro-waveguide structures have beendescribed in particular in patents FR-A-90/02575, FR-A-90/03902 andFR-A-95/00201. More particularly, patent FR-A-90/02575 describes aprocess for connecting the end of an optical fiber issuing from amultifiber optical cable to an integrated optical micro-waveguide in astructure.

The object of the present invention is to provide an optical wavetransmission device for improving and increasing the number of opticalwave transmission channels in a structure so as in particular to providesimplified multichannel switching structures of small size.

According to the present invention, the structure comprises hollowedparts or notches designed to receive and fix therein the end parts of anoptical fiber in such a way that this optical fiber straddles thesurface of the structure separating said hollowed parts and such thatthe ends of the optical fiber are optically coupled to optical guidingmeans of said structure respectively.

According to the invention, said hollowed parts may advantageously beproduced on each side of at least one integrated optical waveguide ofsaid structure, which extends below or is flush with the aforementionedsurface.

According to the invention, at least one of the ends of the opticalfiber may advantageously be optically coupled to integrated opticalguiding means of said structure.

According to one embodiment of the invention, the structure has adeformable part provided with at least one auxiliary optical guidingmeans and an actuating means is designed to move this deformable partbetween a first position and a second position so that an end surface ofthis auxiliary optical guiding means is optically coupled either to oneend of said optical fiber or to an end surface of an integrated opticalwaveguide of said structure which extends below the aforementionedsurface.

According to another embodiment of the invention, the structurecomprises a first integrated optical waveguide which extends below theaforementioned surface and second and third integrated opticalwaveguides which extend to the outside of this surface.

The structure preferably has at least two deformable parts providedrespectively with an auxiliary optical guiding means and is providedwith two actuating means designed to move the respective said deformableparts between a first position and a second position so that, on the onehand, an end surface of a first auxiliary optical guiding means isoptically coupled either to an end surface of the first integratedoptical waveguide or to an end surface of the second integrated opticalwaveguide and, on the other hand, an end surface of a second auxiliaryoptical guiding means is optically coupled either to an end surface ofsaid optical fiber or to an end surface of the third integrated opticalwaveguide.

According to another embodiment of the invention, the structure supportstwo optical fibers and has two integrated optical waveguides. Thestructure has a deformable part provided with at least four auxiliaryoptical guiding means and is provided with an actuating means designedto move this deformable part between a first position and a secondposition so that an end surface of the auxiliary optical guiding meansis optically coupled, selectively and respectively, to the two ends ofthe two optical fibers and the two ends of the two integrated opticalwaveguides.

According to the invention, said deformable part preferably comprisesbranches connected together, each of which is provided with an opticalguiding means.

According to the invention, the end of said optical fiber is preferablyoptically coupled to the end surface of said auxiliary optical guidingmeans via an integrated optical guiding means of the structure.

According to a preferred embodiment of the invention, the deformablepart comprises a cantilevered flexible beam, which supports the one ormore auxiliary optical guiding means longitudinally, and stressing meansfor deforming this beam so as to move its end.

According to the invention, the stressing means preferably comprisecapacitive means or inductive means that deliver a force for stressingsaid beam owing to the effect of an electrical current and/or anelectrical voltage that are delivered by said control means.

The subject of the present invention is also a method for connecting anoptical fiber to an integrated optical micro-waveguide in a structure.

According to the invention, this method consists in:

-   -   fabricating a structure comprising at least one optical        micro-waveguide having one end;    -   hollowing out a notch in the form of a trench in the surface of        said structure in the region of the end of said optical        micro-waveguide by cutting away an end part of this integrated        optical micro-waveguide; and    -   engaging, from above said surface of the structure, and fixing        the end part of the optical fiber in said notch so that the        transmission core of the optical fiber is optically coupled to        the transmission core of the optical micro-waveguide, the fiber        leaving said notch via a curved part.

According to the invention, the method preferably consists in hollowingout a notch, the shape of which provides lateral centering of the endpart of the optical fiber.

According to the invention, the method preferably consists in hollowingout a notch having an end wall through which the optical micro-waveguideemerges and against which the end of the optical fiber bears.

A better understanding of the present invention will be gained bystudying the various optical wave transmission devices described by wayof nonlimiting examples and illustrated by the drawing in which:

FIG. 1 shows a top view of a basic transmission device according to thepresent invention;

FIG. 2 shows a cross section on II—II of the transmission device in FIG.1;

FIG. 3 shows a cross section on III—III of the transmission device inFIG. 1;

FIG. 4 shows a top view of a switching optical wave transmission deviceemploying the device in FIGS. 1 to 3;

FIG. 5 shows a horizontal section of the transmission device in FIG. 4;

FIG. 6 shows a side view of the device in FIG. 4;

FIG. 7 shows a top view of another switching optical wave transmissiondevice employing the device in FIGS. 1 to 3;

FIG. 8 shows a side view of the device in FIG. 7; and

FIG. 9 shows a cross section of the transmission device in FIGS. 1 to 3during fabrication.

FIGS. 1 to 3 show an optical wave transmission device which comprises anintegrated optical guiding structure 2 formed by a block 3 whichcomprises integrated micro-waveguides.

The structure 2 comprises an integrated micro-waveguide 4 that extendslongitudinally, for example between two transverse boundaries 5 and 6 ofthe block 3.

The structure 2 furthermore comprises integrated micro-waveguideconnecting portions 7 and 8 which extend longitudinally from thesurfaces 5 and 6 of the block 3 respectively and which run intolongitudinal notches 9 and 10 provided in the upper face 11 of the block3, on each side of and at a certain distance from the opticalmicro-waveguide 4.

The end surfaces 9 a and 10 a of the notches 9 and 10 that contain endsurfaces of the optical micro-waveguides 7 and 10 face each other andare a certain distance apart.

To make up the structure 2 that has just been described, the block 3comprises a substrate 2 a, for example made of silicon, on which a firstlayer 2 b, for example made of undoped silica, is deposited followed bya second layer 2 c, for example also made of undoped silica. Formed onthe upper face of the layer 2 b and below the layer 2 c are thetransmission cores 4 a, 7 a and 8 a of the optical micro-waveguides 4, 7and 8, for example made of doped silica, or silicon nitride or siliconoxynitride.

As an indication, these transmission cores 4 a, 7 a and 8 a, which arecoplanar, are of rectangular or square cross section and have dimensionsof between 5 and 14 microns. In addition, for making up theaforementioned optical micro-waveguides, the refractive index of thematerial forming their respective transmission cores is higher than therefractive index of the material(s) forming the layers surrounding them.

In a variant, the transmission cores of the optical micro-waveguidescould be flush with the surface of said block, but in general they wouldthus be below this surface.

The device 1 furthermore comprises an optical fiber 12, the end parts 12a and 12 b of which are engaged, via the top of said surface of thestructure, longitudinally in the hollowed-out notches 9 and 10 in such away that its end surfaces are in contact with the faces 9 a and 10 a ofthe notches 9 and 10. These end parts 12 a and 12 b of the optical fiber12 are fixed in the hollowed-out notches 9 and 10, for example bycementing. In the example shown, the optical fiber is not stretched out,rather it has curved parts giving it the definition of a doublecurvature in the form of an elongate S, the fiber leaving the notchesvia two curved parts.

Thus, that part of the optical fiber 12 which extends between its endparts engaged in the notches 9 and 10 from which they emerge upwardstraddles, over a certain distance, the upper surface 11 a of the block11 that separates these notches and below which surface the longitudinalintegrated optical micro-waveguide 4 is provided.

In the example shown, the longitudinal notches 9 and 10 in the block 3are of V-shaped cross section and are hollowed out in such a way thatthe transmission core 12 a of the fiber 12 is, in its end parts 13 and14, in alignment with the transmission cores 7 a and 8 a of theintegrated optical micro-waveguides 7 and 8 respectively.

It follows from the above description that an optical wave traveling inthe integrated optical micro-waveguide 7, the optical fiber 12 and theintegrated optical micro-waveguide 8, in one direction or in the other,passes from one side to the other of the integrated opticalmicro-waveguide 4 in which another optical wave travels, in onedirection or in the other.

FIGS. 4 and 5 show an optical wave transmission device 15 which forms anoptical switching device and employs the optical wave transmissiondevice shown in FIGS. 1 to 3.

This device 15 comprises a structure 16 having optical micro-waveguidesintegrated into a block 17 and formed in the same plane.

A first integrated optical micro-waveguide 18 has a transmission core 18a in the form of an elongate S in such a way that its end parts 19 and20 extend longitudinally and are offset transversely.

A linking integrated optical micro-waveguide 21 has a transmission core21 a which lies in alignment with the end part 20 of the opticalmicro-waveguide 18 and a linking integrated optical micro-waveguide 22has a transmission core 22 a which lies in alignment with the end part19 of the optical micro-waveguide 18. The linking opticalmicro-waveguides 21 and 22 are thus placed on each side of the opticalmicro-waveguide 18 and at a certain distance from the latter.

The facing ends of the integrated optical micro-waveguides 21 and 22 areconnected via an optical fiber 23 as described with reference to FIGS. 1to 3, this fiber straddling the surface of the block 17 below which theintegrated optical waveguide 18 is provided.

Second and third integrated optical micro-waveguides 24 and 25 havetransmission cores 24 a and 25 a which extend longitudinally, on eitherside of the assembly formed by the integrated optical micro-waveguidesas described above.

The structure 16 furthermore includes, on each side of its zone in whichthe assembly comprising the aforementioned optical micro-waveguides andthe optical fiber 23 is provided, four auxiliary integrated opticalmicro-waveguides 26, 28, 30 and 32 which extend longitudinally and canbe selectively connected to the aforementioned optical micro-waveguidesin the following manner.

The transmission core 26 a of the auxiliary optical micro-waveguide 26can be optically coupled either to the transmission core 21 a of thelinking micro-waveguide 21 or to the transmission core 24 a of themicro-waveguide 24 via an optical switch 27.

The transmission core 28 a of the auxiliary optical micro-waveguide 28can be optically coupled either to the transmission core 18 a of themicro-waveguide 18, at the end of its part 19, or to the transmissioncore 25 a of the micro-waveguide 25 via an optical switch 229.

The transmission core 30 a of the auxiliary optical micro-waveguide 30can be optically coupled either to the transmission core 18 a of themicro-waveguide 18, at the end of its part 20, or to the transmissioncore 24 a of the micro-waveguide 24 via an optical switch 31.

The transmission core 32 a of the auxiliary optical micro-waveguide 32can be optically coupled either to the transmission core 22 a of thelinking micro-waveguide 22, or to the transmission core 25 a of themicro-waveguide 25 via an optical switch 33.

An illustrative example of the optical switch 27 will now be describedwith reference to FIG. 5, it being possible for the optical switches 29,31 and 33 to have equivalent structures.

The block 17 has a cavity 34 in which a longitudinal flexible beam 35 iscantilevered from a vertical wall 36 of this cavity 24. The end surface37 of the beam 35, perpendicular to its longitudinal direction, extendsparallel to and a short distance from a vertical surface 38 of thecavity 34 parallel to its vertical wall 5, forming a space 39 betweenthese surfaces 37 and 38.

The optical micro-waveguide 26 a runs along the beam 35 as far as itsend 37.

The optical micro-waveguides 21 a and 24 a open into the cavity 34 onits surface 38.

The flexible beam 35 is provided with an actuating member 40, inparticular as suggested by patent FR-A-90/03902 and is formed moreparticularly in the following manner.

In the cavity 34, the flexible beam 35 has, at a short distance from itsend 37, a lateral arm 41 which supports, on each side, longitudinalbranches 42 and 43 between which respectively extend, at a certaindistance away, branches 44 and 45 made so as to project into the cavity34 from the opposed vertical walls of this cavity.

The facing vertical faces of the branches 42 and 43 on the one hand andof the branches 44 and 45 on the other are coated with metal layers (notshown) so as to form the electrodes of a capacitive or inductive drivingmember 40 a. These electrodes are connected to electrical supply lines(not shown), for example via tracks and/or wire bridges (not shown).

The driving member 40 is designed so as to be capable of beingelectrically controlled in such a way that the flexible beam 35 candeform, in order to occupy two extreme positions in which the endsurface of the transmission core 26 a of the auxiliary opticalmicro-waveguide 26 can be optically coupled either to the end surface ofthe transmission core 21 a of the linking optical micro-waveguide 21 orto the end surface of the transmission core 24 a of the opticalmicro-waveguide 24.

The arrangement shown in FIG. 4 consequently forms an optical switchingdevice for switching two optical channels to two optical channels inwhich the incoming optical waves and the outgoing optical waves travelin the same longitudinal direction.

This is because, by selectively controlling the devices 40 a for drivingthe switches 27, 29, 21 and 34, the optical input/output micro-waveguide26 and 28 may be selectively connected to the auxiliary output/inputoptical micro-waveguide 30 and 32 without any optical waveguide crossingitself because of the existence of the optical fiber 23 whichconstitutes a bridge for passing above the optical micro-waveguide 18.

An optical wave transmission device 46 will now be described withreference to FIG. 6, said device forming an optical switching device andalso employing the structure of the optical wave transmission devicedescribed previously with reference to FIGS. 1 to 3.

The block 47 a with integrated optical micro-waveguides of the structure48 of the device 46 has a cavity 49 in which, as in the exampledescribed with reference to FIG. 5, a cantilevered longitudinal beamlies, which beam, this time, comprises four longitudinal branches 51,52, 53 and 54 spaced apart transversely, the end surfaces of which lie ashort distance from a transverse wall 55 of the cavity 49. Thus, thestiffness of the beam 50 may be determined by the cross sections of itsbranches 51-54.

The branches 51-54 of the beam 50 have, longitudinally and right totheir aforementioned ends, the transmission cores 56 a, 57 a, 58 a and59 a of four integrated auxiliary optical micro-waveguides 56, 57, 58and 59.

Near their ends, the branches 51-54 of the beam 50 are connected viatransverse members 60, 61 and 62. The lateral branch 54 supports alateral arm 63 connected to an actuating member 64, for example oneequivalent to the actuating member 40 of the example described withreference to FIG. 5.

Thus, as in that example, the ends of the branches 51-54 forming thebeam 50 can be moved horizontally, facing the surface 55 of the cavity49, by the driving member 64.

The structure 48 furthermore includes, in that part of the block 47facing the end of the beam 50, two integrated optical micro-waveguides65 and 66 whose transmission cores 65 a and 66 a form horseshoe-shapedloops and whose ends open longitudinally into the cavity 49 through itswall 55, facing the ends of the branches 51 and 52 on the one hand and53 and 54 on the other, respectively.

Provided near the four end parts of the integrated opticalmicro-waveguides 65 and 66 are four linking optical micro-waveguides 67,68, 69 and 70 whose transmission cores 67 a, 68 a, 69 a and 70 a extendlongitudinally open into the cavity 49 through its wall 55.

The linking optical micro-waveguides 67 and 70 on the one hand and thelinking optical micro-waveguides 68 and 69 on the other are opticallyconnected by optical fibers 71 and 72 according to the arrangementsdescribed with reference to FIGS. 1 to 3.

These optical fibers 71 and 72 are curved in the form of a horseshoe andpass above the surface of the block 47 in such a way that the opticalfiber 71 straddles the integrated optical micro-waveguide 65 and theoptical fiber 72 straddles the integrated optical micro-waveguide 66.

The driving member 64 is designed to deform the beam 50 in such a waythat its branches 51-54 connected via the cross members 60-62 can movebetween two extreme positions.

When the beam 50 is in one extreme position, the optical micro-waveguide56 of the branch 51 is optically connected to the opticalmicro-waveguide 59 of the branch 54, via the linking opticalmicro-waveguides 67 and 70 and the optical fiber 71, and the opticalmicro-waveguide 57 of the branch 52 is optically connected to theoptical micro-waveguide 58 of the branch 53, via the linking opticalmicro-waveguides 68 and 69 and the optical fiber 72.

When the beam 52 is in its other extreme position, the opticalmicro-waveguide 56 of the branch 51 and the optical micro-waveguide 57of the branch 52 are optically connected via the optical micro-waveguide65 and the optical micro-waveguide 58 of the branch 53 is opticallyconnected to the optical micro-waveguide 59 of the branch 54 via theoptical micro-waveguide 66.

The arrangement shown in FIG. 7 consequently forms an optical switchingdevice for switching two optical channels to two optical channels, inwhich the incoming and outgoing optical waves travel longitudinally inopposite directions via the beam 50.

The manner in which the longitudinal notches 9 and 10 of the block 3 ofthe integrated structure 2, described with reference to FIGS. 1 to 3,may be fabricated will now be described with reference to FIGS. 8 and 9,taking the notch 9 as example.

A block 3 a comprising the micro-waveguide 7 is fabricated, thetransmission core 7 a of said micro-waveguide having an end 7 b locatedin the region of the notch 9 to be produced and at a certain distancefrom the edges of the surface of the structure.

Next, using a photolithography and etching process, the trench-shapednotch 9 is hollowed out in such a way that this operation cuts away, forexample by a few microns, the end part 7 c of the transmission core 7 a,forming the end surface 9 a and an opposed end surface, which extendperpendicular to the longitudinal direction of this core 7 a and of thenotch 7, and the longitudinal surfaces for the lateral support of theoptical fiber, the edges of the notch not reaching the edges of thesurface 11 of the structure.

Thus, positioning the notch 7 is not affected by the position of the end7 b of the transmission core 7 a. In addition, the end surface of thistransmission core 7 a may coincide exactly with the end wall 9 a of thenotch 7 in such a way that the optical coupling between the transmissioncore 7 a and the transmission core 12 a of the optical fiber 12 may beof excellent quality.

In another application example (not shown) of the arrangements in FIGS.1 to 3, an integrated structure could comprise two input channels andtwo output channels between which would be respectively placed anoptical demultiplexer, each of the lines of which transmit one or moreparticular wavelengths, and an optical multiplexer. Using one or moreoptical fibers mounted as described above, it would be possible toextract an optical wave at a given wavelength from one line of one ofthe input channels so as to introduce it into the other output channel.

Such an arrangement thus constitutes a switch for switching part of anoptical wave from one channel to another channel.

The present invention is not limited to the examples described above.Many alternative embodiments are possible without departing from thescope defined by the appended claims.

1. An optical wave transmission device comprising an integratedstructure having integrated optical wave guiding means, characterized inthat the structure comprises hollowed parts or notches (9, 10) made oneach side of at least one integrated optical guiding means (4) whichextends below or is flush with a surface (11 a) of the structure andseparating said hollowed parts, in that said hollowed parts or notches(9, 10) are designed to receive and fix therein the end parts (13, 14)of an optical fiber that straddles said surface (11 a) and in that theends of said optical fiber are optically coupled to integrated opticalguiding means (7, 8), respectively.
 2. The device as claimed in claim 1,characterized in that the structure has a deformable part (35) providedwith at least one auxiliary optical guiding means (26) and in that anactuating means (40) is designed to move this deformable part between afirst position and a second position so that an end surface of thisauxiliary optical guiding means is optically coupled either to one endof said optical fiber or to an end surface of an integrated opticalwaveguide of said structure which extends below the aforementionedsurface.
 3. The device as claimed in claim 1, characterized in that thestructure comprises a first integrated optical waveguide (18) whichextends below the aforementioned surface and second and third integratedoptical waveguides (24, 25) which extend to the outside of this surface,in that the structure has at least two deformable parts (27, 29)provided respectively with an auxiliary optical guiding means and inthat the structure is provided with two actuating means designed to movethe respective said deformable parts between a first position and asecond position so that, on the one hand, an end surface of a firstauxiliary optical guiding means is optically coupled either to an endsurface of the first integrated optical waveguide or to an end surfaceof the second integrated optical waveguide and, on the other hand, anend surface of a second auxiliary optical guiding means is opticallycoupled either to an end surface of said optical fiber or to an endsurface of the third integrated optical waveguide.
 4. The device asclaimed in claim 1, characterized in that the structure supports twooptical fibers (71, 72) and has two integrated optical waveguides (65,66), in that the structure has a deformable part (50) provided with atleast four auxiliary optical guiding means (56-59) and in that thestructure is provided with an actuating means (64) designed to move thisdeformable part between a first position and a second position so thatan end surface of the auxiliary optical guiding means is opticallycoupled, selectively and respectively, to the two ends of the twooptical fibers and the two ends of the two integrated opticalwaveguides.
 5. The device as claimed in claim 4, characterized in thatsaid deformable part (50) comprises branches (51-54) connected together,each of which is provided with an optical guiding means (56-59).
 6. Thedevice as claimed in claim 2, characterized in that the end of saidoptical fiber is optically coupled to the end surface of said auxiliaryoptical guiding means via an integrated optical guiding means (67-70) ofthe structure.
 7. The device as claimed in claim 2, characterized inthat the deformable part comprises a cantilevered flexible beam (35;50), which supports the one or more auxiliary optical guiding means (26;56, 59) longitudinally, and stressing means (40; 64) for deforming thisbeam so as to move its end.
 8. The device as claimed in claim 7,characterized in that the stressing means comprise capacitive means orinductive means (40 a) that deliver a force for stressing said beamowing to the effect of an electrical current and/or an electricalvoltage that are delivered by control means.
 9. The device as claimed inclaim 3, characterized in that the end of said optical fiber isoptically coupled to the end surface of said auxiliary optical guidingmeans via an integrated optical guiding means (67-70) of the structure.10. The device as claimed in claim 4, characterized in that the end ofsaid optical fiber is optically coupled to the end surface of saidauxiliary optical guiding means via an integrated optical guiding means(67-70) of the structure.
 11. The device as claimed in claim 5,characterized in that the end of said optical fiber is optically coupledto the end surface of said auxiliary optical guiding means via anintegrated optical guiding means (67-70) of the structure.
 12. Thedevice as claimed in claim 3, characterized in that the deformable partcomprises a cantilevered flexible beam (35; 50), which supports the oneor more auxiliary optical guiding means (26; 56, 59) longitudinally, andstressing means (40; 64) for deforming this beam so as to move its end.13. The device as claimed in claim 4, characterized in that thedeformable part comprises a cantilevered flexible beam (35; 50), whichsupports the one or more auxiliary optical guiding means (26; 56, 59)longitudinally, and stressing means (40; 64) for deforming this beam soas to move its end.
 14. The device as claimed in claim 5, characterizedin that the deformable part comprises a cantilevered flexible beam (35;50), which supports the one or more auxiliary optical guiding means (26;56, 59) longitudinally, and stressing means (40; 64) for deforming thisbeam so as to move its end.
 15. The device as claimed in claim 6,characterized in that the deformable part comprises a cantileveredflexible beam (35; 50), which supports the one or more auxiliary opticalguiding means (26; 56, 59) longitudinally, and stressing means (40; 64)for deforming this beam so as to move its end.